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Gluten Free Peanut Butter Sheet Cake Bars

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Is there anything better than the classic combination of rich, decadent chocolate and creamy peanut butter? Gluten Free Peanut Butter Sheet Cake Bars are an easy and delicious take on this ultimate flavor mashup.

Gluten Free Peanut Butter Sheet Cake Bars

From no-bake desserts like Gluten Free Chocolate Chip Cookie Peanut Butter Pie to this tender and moist peanut butter cake, peanut butter is a food group unto itself. With its ooey gooey double layer of frosting, this is sure to become a new favorite.


All good things start with peanut butter including these Gluten Free Peanut Butter Sheet Cake Bars. Combining pantry staples with a couple of easy short cuts this dessert is as easy to shop for as it is delicious to eat.

  • Sugar
  • Dairy Free Butter – Make sure that your butter is at room temperature. This will allow the batter to come together easily without over mixing it.
  • Creamy Peanut Butter – Not only infuses the slightly savory flavor of peanuts into every bite but also makes this cake rich, tender, and moist.
  • Eggs Just like leaving the butter out at room temperature helps this batter come together easily, the same holds true for the eggs as well.
  • Dairy Free Sout Cream – Adds tang to balance the sweetness and richness while also keeping this cake moist.
  • Dairy Free Milk – Use your favorite unsweetened Dairy Free milk. I like oat milk for this recipe.
  • Vanilla Extract – The better the quality the vanilla extract, the more pronounced the flavor.
  • Gluten Free Flour – Bob’s Red Mill Gluten Free 1 to 1 Baking Flour is my favorite for both sweet and savory recipes. Especially in recipes not originally written as Gluten Free it makes it easy to measure without having to add any additional ingredients.
  • Baking Powder
  • Baking Soda
  • Kosher Salt – Enhances all of the flavors of the ingredients.
  • Marshmallow Fluff – This childhood favorite is also a classic pairing with peanut butter for that fluffernutter flavor combination.
  • Chocolate Frosting – Take the help of the grocery store and use your favorite Dairy Free chocolate frosting. Combined with the marshmallow fluff it’s an over-the-top crown for this peanut butter cake.
  • Toasted Peanuts While this is completely optional, toasted peanuts add crunch and texture to every bite.

How to Make Gluten Free Peanut Butter Sheet Cake Bars

Baking a cake from scratch has never been easier than with this decadent and rich peanut butter cake. With just a few simple steps your friends and family are sure to fall in love with these peanut butter bars.

Time needed: 2 hours and 45 minutes

Peanut butter cake is frosted with both marshmallow fluff and sumptuous chocolate frosting.

  1. Pregame

    Preheat the oven to 350 degrees. Spray a 9×13 cake pan with nonstick baking spray and set it aside.

  2. Batter Up

    Add the peanut butter, butter, and sugar to a bowl and mix on high for 5 minutes until it is light and fluffy. Add in the eggs, sour cream, and milk and mix until just combined. Add the dry ingredients and mix until just combined, careful not to over mix.

  3. Bake

    Spread the batter into the prepared baking dish. Let the cake bake for 30-35 minutes or until a toothpick comes out clean.

  4. Cool Down

    Allow the cake to cool completely before frosting.

  5. Crowning Touch

    Spread the marshmallow fluff over the top of the cake. Heat up your chocolate frosting so it can be drizzled over the top. Drizzle a solid layer of chocolate frosting over the marshmallow fluff and garnish with peanuts. Slice and enjoy!


Don’t be afraid to mix things up! This recipe can also be made into cupcakes, using the chocolate frosting and marshmallow fluff on top. You can also fill the cupcakes with the marshmallow fluff if desired.


With so many allergens and food sensitivities, I am always looking for ways to make my recipes accessible to everyone. If you or one of your friends or family have a tree nut allergy, the peanut butter in this recipe can be replaced with sunflower seed butter.

In addition to providing its own unique flavor that is a great swap for peanut butter, sunflower seed butter also offers up additional nutrients. It’s rich in protein, vitamin E, fiber, zinc, and iron.

This recipe is completely Dairy Free. However, you can use full dairy products in this recipe.


Using a stand mixer or hand mixer helps this batter come together with ease. In addition, you will need a 9×13 cake pan for this recipe.

Top Tip for Gluten Peanut Butter Sheet Cake Bars

Whether working with Gluten Free flour or full gluten flour in cakes, you never want to over mix your batter. Allowing all of your ingredients to come to room temperature sure as the butter, eggs, and sour cream, makes it easier to mix the batter together quickly and keep it smooth and lump free.

Gluten Free Flours

There are so many more quality Gluten Free options widely available these days. I wanted to quickly share with you some of the types I like to use and have had success with.

My go to for baking is Bob’s Red Mill 1:1. It is a blend of several different gluten free ingredients and I find it just works consistently well for what I need. I could blend flour myself but I choose to spend my time other ways and the 1:1 is a really good product.

Oat Flour can give you a chewier, more moist product. It can lend a nice sweet flavor to baked foods and is a flour I tend to mix with others if I want a lighter or fluffy result. I am always very careful to buy organic gluten free oats because they can be sprayed with nasty stuff and be processed in a way that they are no longer gluten free.

Almond Flour has a nice nutty flavor but can tend to dry out what you are preparing. I like to balance it with an extra egg if I am adding it to meatloaf for example and add banana or egg if it is in a sweet treat. Your end product could be a bit denser if you are using straight almond flour as well. I do like using almond flour as bread crumbs or a crunchy topping on savory dishes. 

Arrowroot  is my normal choice for a thickener in sauce or gravy. It is great for things you want a good crunch on that would normally be dredged in flour. Arrowroot can also be used to temper other gluten free flours for sweets and baked goods.

Brown Rice Flour can also be used in combination with other gluten free flours for baked goods. I like to use it when making a roux and brown rice noodles are a favorite.

Amaranth is another gluten free flour that works well when blended. It has a nice nutty flavor that makes it good for crusts, tortillas and breads.

Coconut Flour has a bit of a sweet coconut flavor. It tends to absorb liquid so you will need to adjust your recipe but it does give a nice light texture.

Corn Flour is a great thickener, makes delicious tortillas and one of my favorites, corn bread. Just make sure the corn flour you are buying was proceed in a gluten free environment and from a clean source.

Cassava Flour is the most similar to white or all purpose flour but can be expensive if you are using it often and is high in carbohydrates.

Tapioca is a great thickener as well for soups, pies and sauces and works well when combined with other flours.

Chickpea or garbanzo is used often in Indian and Middle Eastern cuisine… Think hummus, falafel, flatbreads. It has lots of healthy benefits and a mild nutty flavor. You can also use the water from the beans, called aquafaba, as an egg replacer or instead of cream for whipped cream. Crazy, I know, but it works so stop dumping it down the drain.  

Gluten Free Grains

The gluten free grains we grab for most often are…

Quinoa- easy to make and flavor and is high in fiber and protein. It is actually one of the plant proteins that is a complete protein. 

Oats are also good for fiber and a bit of protein but make sure they are clean and gluten free.

Buckwheat actually has no wheat in it but does have fiber, protein and trace minerals. I love buckwheat noodles. I also add them to salads and soups for texture and a bit of “chew”.

Gluten Free Peanut Butter Sheet Cake Bars

Gluten Free Peanut Butter Sheet Cake Bars

Rich and moist peanut butter cake is topped with marshmallow fluff and chocolate frosting.
Print Pin Rate
Course: Dessert
Prep Time: 10 minutes
Cook Time: 35 minutes
Servings: 12


  • 1 mixing bowl/mixer
  • 1 9×13 cake pan


Peanut Butter Cake

  • 1 2/3 cups sugar
  • 1/2 cup butter, room temperature
  • 2 eggs, room temperature
  • 1 cup peanut butter
  • 1/2 cup sour cream
  • 1 cup milk
  • 2 tsp vanilla extract
  • 2 cups 1.1 flour
  • 1 1/2 tsp baking powder
  • 1 1/2 tsp baking soda
  • 1/2 tsp kosher salt


  • 16 oz marshmallow fluff
  • 16 oz Dairy Free chocolate frosting
  • 1 cup toasted peanuts, optional


  • Preheat oven to 350 degrees. Spray a 9×13 baking dish with nonstick baking spray and set aside.
  • Add the peanut butter, butter, and sugar to a bowl and mix on high for 5 minutes.
  • Add the milk, sour cream, eggs, and vanilla and mix to combine.
  • Add the dry ingredients and mix until just combined.
  • Spread the batter into the prepared cake pan.
  • Bake for 30-35 minutes or until a toothpick comes out clean. Allow to cool completely.
  • Spread the marshmallow fluff over the top of the peanut butter cake.
  • Heat up the chocolate frosting until it loosens up a little. Drizzle a solid layer of chocolate frosting over the top of the marshmallow fluff.
  • Garnish with toasted peanuts if desired.
  • Cut and enjoy!
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